Portland, Maine climate: Normal weather by month, frost dates and records
Portland's normal year runs from 16°F January nights to 80°F July afternoons, with 48.1 inches of precipitation and 69 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.6°C, January lows of −9°C, July highs of 26°C, 1,222 mm of precipitation a year.
- NOAA stationPortland International Jetport
- Station IDUSW00014764
- Location43.65°N 70.30°W
- Elevation45 ft (14 m)
- From the center6 miles
- Population69,568
On October 22, the normal high in Portland is 57°F and the normal low 39°F, and the chance of measurable rain or snow is 35%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Portland.
- Jan 32° 16°
- Feb 35° 17°
- Mar 42° 26°
- Apr 54° 35°
- May 64° 46°
- Jun 74° 55°
- Jul 80° 61°
- Aug 79° 60°
- Sep 71° 52°
- Oct 60° 41°
- Nov 48° 32°
- Dec 38° 22°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Portland each month?
July is the warmest month, with normal highs of 80°F; January the coldest, with normal lows of 16°F. The most precipitation falls in October (5.25 in), the least in July (3.43 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 32°F | 16°F | 24.0°F | 3.50 | 18.6 | 11 | <1 | 29 | 9 h 20 min |
| February | 35°F | 17°F | 26.2°F | 3.54 | 16.6 | 10 | <1 | 26 | 10 h 30 min |
| March | 42°F | 26°F | 34.1°F | 4.08 | 13.6 | 11 | <1 | 25 | 11 h 50 min |
| April | 54°F | 35°F | 44.6°F | 4.41 | 2.8 | 11 | <1 | 12 | 13 h 20 min |
| May | 64°F | 46°F | 54.9°F | 3.67 | 0.0 | 13 | <1 | 1 | 14 h 40 min |
| June | 74°F | 55°F | 64.3°F | 4.15 | 0.0 | 12 | 1 | <1 | 15 h 20 min |
| July | 80°F | 61°F | 70.4°F | 3.43 | 0.0 | 11 | 2 | <1 | 15 h 10 min |
| August | 79°F | 60°F | 69.2°F | 3.57 | 0.0 | 9 | 1 | <1 | 14 h |
| September | 71°F | 52°F | 61.6°F | 3.77 | 0.0 | 9 | 1 | <1 | 12 h 30 min |
| October | 60°F | 41°F | 50.3°F | 5.25 | 0.2 | 11 | <1 | 6 | 11 h 10 min |
| November | 48°F | 32°F | 40.0°F | 4.25 | 2.3 | 11 | <1 | 18 | 9 h 40 min |
| December | 38°F | 22°F | 30.3°F | 4.50 | 14.6 | 12 | <1 | 27 | 9 h |
| Year (annual) | 56°F | 39°F | 47.5°F | 48.12 | 68.7 | 131 | 5 | 144 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 0°C | −9°C | −4.4°C | 89 mm | 47 cm |
| February | 2°C | −8°C | −3.2°C | 90 mm | 42 cm |
| March | 6°C | −3°C | 1.2°C | 104 mm | 35 cm |
| April | 12°C | 2°C | 7.0°C | 112 mm | 7 cm |
| May | 18°C | 8°C | 12.7°C | 93 mm | 0 cm |
| June | 23°C | 13°C | 17.9°C | 105 mm | 0 cm |
| July | 26°C | 16°C | 21.3°C | 87 mm | 0 cm |
| August | 26°C | 15°C | 20.7°C | 91 mm | 0 cm |
| September | 22°C | 11°C | 16.4°C | 96 mm | 0 cm |
| October | 15°C | 5°C | 10.2°C | 133 mm | 1 cm |
| November | 9°C | 0°C | 4.4°C | 108 mm | 6 cm |
| December | 3°C | −5°C | −0.9°C | 114 mm | 37 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014764; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Portland?
Normal highs sit between 65°F and 85°F in June, July, August and September. Of those, September has the fewest days with rain (9).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014764.
When is the last frost in Portland?
In Portland, the last spring frost (32°F) comes after April 26 in half of years and after May 7 in one year in ten; the first autumn frost comes before October 15 in half of years and before October 2 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 261 year in 10 after May 7; 9 in 10 after April 16
- First autumn frost, half of years before
- October 151 year in 10 before October 2; 9 in 10 before October 30
NOAA puts the median frost-free season at 170 days, and the season without a hard freeze (28°F) at 195 days.
A hard freeze (28°F) comes after April 14 in half of springs and before October 27 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Portland in zone 6a across its 6 ZIP code areas (6a in 04103, the largest). By the map's own method, the average of each year's coldest night over 1991-2020, Portland's NOAA station is in zone 6a: the coldest night of a typical year reaches −9°F (30 complete years).
Frost dates for every NOAA station in Maine · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00014764; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
What hardiness zone is each Portland ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Portland's 6 ZIP code areas are all in zone 6a. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Portland?
In a normal year in Portland, 5 days a year reach 90°F, 144 nights fall to 32°F or colder and 131 days bring measurable precipitation.
- Days at 90°F or more
- 5a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 144a normal year
- Days that stay below freezing
- 41high of 32°F or less
- Days with 0.01 inch of precipitation
- 131a normal year
- Days with 1 inch of snow or more
- 16a normal year
The highest temperature in Portland's official record (kept by the National Weather Service since 1874) is 103°F, on July 4, 1911; the lowest is −39°F, on February 16, 1943.
The wettest calendar year on that record is 2005, with 66.40 in; the snowiest season is 1970–71, with 141.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00014764; records: ACIS (NOAA Regional Climate Centers), NWS threaded record PWMthr. Records use complete months only; a month missing more than three days is left out.
How humid and windy is Portland, and how clear are its skies?
The summer (June-August) dew point averages 59°F. The muggiest month is July, with an average dew point of 61°F; the driest air comes in January (13°F). March is the windiest month (9.2 mph on average), and August has the most clear or nearly clear hours (61%).
| Month | Dew point | Humidity | Afternoon humidity | Wind | Clear or few clouds | Overcast |
|---|---|---|---|---|---|---|
| January | 13°F | 62% | 50% | 8.0 mph | 54% | 32% |
| February | 18°F | 62% | 53% | 9.1 mph | 48% | 38% |
| March | 27°F | 62% | 50% | 9.2 mph | 47% | 39% |
| April | 37°F | 64% | 51% | 8.5 mph | 47% | 37% |
| May | 49°F | 72% | 60% | 7.5 mph | 43% | 37% |
| June | 58°F | 72% | 58% | 6.9 mph | 55% | 24% |
| July | 61°F | 74% | 60% | 6.3 mph | 56% | 22% |
| August | 57°F | 73% | 57% | 6.5 mph | 61% | 19% |
| September | 48°F | 75% | 60% | 6.8 mph | 56% | 29% |
| October | 36°F | 71% | 57% | 7.8 mph | 49% | 36% |
| November | 26°F | 70% | 59% | 7.8 mph | 49% | 38% |
| December | 17°F | 67% | 56% | 7.8 mph | 51% | 35% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00014764. Monthly averages of all hours; afternoon humidity at 3 p.m. local standard time; sky as the share of hours NOAA's observations rate clear or few clouds (a dash where NOAA publishes no sky value).
How sunny is Portland?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Portland, 3.8 kWh per square metre a day. August is the sunniest month (79%) and December the cloudiest (64%). Among the 459 U.S. places of 50,000 or more, that ranks tied 385th (with 30 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 67% | 1.7 |
| February | 69% | 2.5 |
| March | 69% | 3.6 |
| April | 70% | 4.7 |
| May | 69% | 5.3 |
| June | 70% | 5.6 |
| July | 77% | 5.9 |
| August | 79% | 5.3 |
| September | 78% | 4.3 |
| October | 70% | 2.8 |
| November | 68% | 1.8 |
| December | 64% | 1.4 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Portland need?
A normal year in Portland brings 6,795 heating degree days, 26% more than the median U.S. place (5,373), and 447 cooling degree days, 51% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,327 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,271 | 0 |
| February | 1,088 | 0 |
| March | 956 | 0 |
| April | 613 | 1 |
| May | 325 | 10 |
| June | 89 | 68 |
| July | 10 | 176 |
| August | 16 | 147 |
| September | 145 | 43 |
| October | 459 | 2 |
| November | 749 | 0 |
| December | 1,074 | 0 |
| Year (annual) | 6,795 | 447 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014764. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Portland been warmer than normal lately?
2025 averaged 46.8°F, 0.7°F below the 1991-2020 normal of 47.5°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 48.8°F | +1.3°F | 44.92 | 33.4 |
| 2022 | 48.2°F | +0.7°F | 46.66 | 36.6 |
| 2023 | 48.8°F | +1.3°F | 56.67 | 52.5 |
| 2024 | 49.1°F | +1.6°F | 46.32 | 43.3 |
| 2025 | 46.8°F | −0.7°F | 37.90 | 60.7 |
Over 81 complete years from 1942 to 2025, the station's annual mean temperature rose at a fitted 4.1°F per century (+0.23°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00014764; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Portland's climate compare?
Portland is warmer than 41 of the other 41 places with their own NOAA record in Maine, and wetter than 27. Across the 7,247 U.S. stations with normals, its annual mean of 47.5°F is warmer than 30%.
In the Köppen classification computed from these normals, Portland is Dfb: continental, no dry season, warm summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Portland share this climate record?
9 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- South Portland, ME26,994 people · 1 mi SE
- Westbrook, ME21,386 people · 5 mi NW
- Saco, ME21,064 people · 10 mi SW
- Old Orchard Beach, ME9,438 people · 9 mi S
- Gorham, ME18,545 people · 7 mi NW
- Oak Hill, ME5,365 people · 4 mi SW
- Falmouth Foreside, ME2,148 people · 7 mi NE
- Dunstan, ME1,916 people · 7 mi SW
- Falmouth, ME12,919 people · 6 mi NE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Portland's climate
What is the coldest month in Portland?
January, with a normal high of 32°F and a normal low of 16°F. The warmest is July (80°F by day, 61°F at night).
Does it snow in Portland?
Yes: 69 inches in a normal year, falling on 29 days with 0.1 inch or more, the most in January (18.6 inches).
What is the rainiest month in Portland?
October, with 5.25 in of precipitation in a normal year; the driest is July with 3.43 in.
What plant hardiness zone is Portland in?
The USDA's 2023 map puts Portland in zone 6a across its 6 ZIP code areas (6a in 04103, the largest). By the same method at Portland's NOAA station, the coldest night of a typical year reaches −9°F (30 years, 1991-2020): zone 6a.
How late can frost come in Portland?
In half of years the last 32°F night comes after April 26; in one year in ten it comes after May 7. Waiting until May 7 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Portland in OctoberThis month day by day, its records and recent years
- Maine climateThe statewide normals and every place in the state
- West Buxton (2 mi NNW), ME16 miles from this station, 45.6°F a year
- Windham (2 mi NW), ME17 miles from this station, 45.7°F a year
- Gray, ME17 miles from this station, 46.3°F a year
- Hollis, ME19 miles from this station, 44.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made